Bill Gates' digital dream palace near Seattle may be the early leader in the race to build the ultimate wired home. But that doesn't leave everyone else out in the cold. Many homes already have several isolated mini-networks. For instance, despite an octopus of cables linking peripherals, the desktop computer may rarely hook up to anything else. Cables running every which way hide behind the entertainment center, but none go to the computer. The security system is a separate wiring array as is any sort of lighting control.

Getting these islands to communicate not just with one another, but also with the outside world via broadband Internet links, is a major effort at a host of electrical and telecommunications equipment companies. They all see big profits in this market. According to the Cahners In-Stat Group, the worldwide home-networking equipment and residential gateway market is expected to grow from more than $600 million in 2000 to more than $5.7 billion by 2004.

"From a market that a couple of years ago was seen as only a small niche to be served by networking equipment companies, today we see every company in the consumer electronics and PC industries, as well as the service providers, developing products and strategies for the connected home," said Mike Wolf, senior analyst for Cahners In-Stat Group. "All aspects of this connected home-communications, entertainment and home systems management-will be interconnected in the future using networking and Internet technology." The resulting demand will require a huge expansion in bandwidth for all communications wires entering a home. More people want to network their homes these days, even if it's just to lay the groundwork for the future.

Competition allows consumers to have a choice among different service providers, creating the need for easier switching and access to services. This demand may also stimulate development of a relatively new type of residential network product called a "gateway," which is a box or a device to provide an interface between the home wiring and the incoming services- whatever they may be.

To understand what a network is, let's look at the ISO OSI reference model for network protocols, which involves seven layers. The layers of the "stack" are depicted in Fig. 1 on page 14. Every product, device or service needs a way to physically get bits (voltage/current) from one place to another. This is done on what is called the physical layer or physical interface. The next layer up defines the rules for carrying the information through the media. A group of bits (information) is sent in what is called a data packet that's organized in a certain way. A header is at the beginning of the packet and includes the destination address. In addition, the data packet must be able to retransmit and correct errors. For that reason, only 60% of a typical Ethernet data packet is considered payload, or information; the rest is called overhead, or the packaging material.

In addition, there is typically some kind of language prescribed. Devices have to know the rules and what to say to each other-commands, status, requests and so on.

Rules to define how the language will be used-who is going to say what to whom (for example, between a PC and a security sensor, in delivering information). Networks also must allow different products to define what they do and identify other products on the network. This is where an "interoperability specification" comes in. Interoperability means that different systems can "talk" to each other.

Following the invention of X-10 in 1978, little happened in home-automation until the technology of CEBus, LonWorks and then in early 1996, the audio/video (A/V) industry's 1394 network specification. Since then, a number of other technologies have emerged, with interoperability remaining a key concern. Why interoperability? Each of the industry groups-television, computers, home automation-has different technical requirements. The audio/visual industry, for example, in converting from analog to digital, needs enormous bandwidth. The computer industry has less stringent requirements-it needs medium to high bandwidth. Home automation has low bandwidth needs for control applications-typically 15 Kbit/sec to 50 Kbit/sec. The result is that each of these three industry groups promotes its own network technology solution, which can be completely isolated from the others. Most of these technologies are in the physical layer.

Twisted-pair copper wiring It looks like good quality four-pair, unshielded twisted-pair (UTP) telephone wiring is going to be a key ingredient in structured home wiring because of the increasing emphasis on telecom standards. Electrical contractors and engineers are becoming familiar with the Telecommunications Industry Association (TIA), which developed a series of standards for structured network wiring in commercial office buildings during the late 1980s. At that time, the EIA/TIA-568 Commercial Building Telecommunications Wiring Standard, which covers the planning and installation of building wiring independent of the telecom hardware and components that will be installed, was issued.

The TIA also developed a standard for residences, called the TIA-570 Residential Telecommunications Cabling Standard. This document was basically ignored because it was rather sketchy and incomplete. However, the less than two-year-old TIA-570-A revision of the standard has caught up with residential infrastructure wiring practices and it's getting attention. Because it embraces at least three different media, the telecom-oriented 570-A document emerges as the closet thing to a bona fide standard for a residential network. Contractors and installers involved in residential work should have this document, which is sold by Global Engineering Documents. Orders are taken by phone at (800) 624-3974, by fax at (303) 379-7935, and on the Web at www.global.ihs.com.

Covering basic single-family and multi-family infrastructure wiring, 570-A mentions the installation of a distribution device, but the term is not defined, other than saying it should support the interconnection of cabling and a star wiring topology. The 570-A standard also defines two grades of service. Grade 1 meets the minimum requirements for telecommunications. Examples of applications for this specification include telephone, satellite, community antenna television (CATV) and data services. Grade 1 specifies a minimum of four-pair Cat. 3 cable and Series 6 coaxial cable placed in a star topology. Grade 2 provides for both current and developing telecommunications services, especially for multimedia usage. Grade 2 specifies two four-pair Cat. 5 UTP cables, and two RG-6 coaxial cables. One of the Cat. 5 cables is for voice and the other is for data. One of the RG-6 cables is for satellite service and the other is for local programming via a rooftop antenna or cable TV connection. Glass optical fiber cable is an option.

The total cabling system within a home infrastructure or cabling layout should include adequate space for the distribution device, and the cabling must follow a star topology.

Twisted-pair copper cabling is robust enough to support a typical Ethernet network connecting computers and peripherals. And, with recently developed methods, Cat. 5 UTP cabling offers the prospect of up to 1,000-Mbit/sec speeds-enough to carry high-quality video. Carrying only digital signals and capable of supporting data rates of more than 1,000-Mbit/sec, multimode optical fiber has a distinct advantage in distances greater than 100 meters (300 ft). In the future, plastic optical fiber may also be used when its distance performance improves.

The IEEE 1394 standard Some industry groups cooperated in developing the IEEE-1394-1995 standard, also called FireWire. First conceived by Apple Computer, FireWire allows information from broadcast, cable or satellite TV, and even from the Internet, to be sent to a TV or other electronic product.

FireWire uses a special shielded cable with six individual conductors: one for power, one for ground, two for data and two for strobe, which synchronizes the data. Any single device (which is called a node) can be used to control all the others. Every device houses a transceiver, and all transceivers, which are connected together in a serial bus, must be turned on, or powered, all the time. The 1394 standard was originally developed to interconnect A/V equipment over short distances in a cluster or group, such as a home theater or home entertainment system.

For whole house applications, a trade organization called the Video Electronic Standards Association (VESA) has been working on a home-automation-oriented, high-speed data network based on 1394, called 1394b.

The 1394b version uses twisted pair and fiber (no coax) for up to 800 Mb/sec transfers over distances up to 100 meters. While primarily intended for A/V applications, the VESA spec can be used for anything-computer networks, home automation, etc. It is about the closest thing there is to a high-speed whole house network.

To wire a house for a 1394b network, home runs not exceeding 100 meters of Cat. 5 cabling, or better, are installed from a central distribution point. Alternately, fiber can be used for a distance of 200 plus meters (perhaps to 500 meters).

Control networks require very low speed transmission-not much over 10kbits/s-and several companies have reliable schemes to transmit such data rates over a home's ac wiring.

The two most important control technologies are the Consumer Electronics Bus (CEBus) and LonWorks, because both use a peer-to-peer architecture and rely on relatively simple network protocols that work with microcontrollers.

The EIA-600 CEBus Standard for Consumer Electronic Bus, developed by the Electronic Industries Alliance (EIA) provides a communications and control network. This standard allows for a variety of media types to be used: twisted-pair, coaxial and fiber-optic cable, power-line carrier, infrared devices and radio-frequency (RF) transmission. It can handle: remote control, status indication, energy management, entertainment device coordination and A/V distribution.

The first power-line carrier technology for the home was the X-10 system. Wall switches and receptacles containing X-10 technology were simple enough for consumers to set up the control systems themselves. Unfortunately, the reliability of X-10's simple protocol varies significantly among installations. To improve reliability, X-10 has made many refinements over the years and has retained its simple modulation scheme and generally has kept new units compatible with older products. Unlike CEBus and LonWorks, X-10 is not an ANSI standard, and therefore is not considered an "open" standard.

Opportunity for low-voltage installers Think of the ANSI/TIA/EIA 570-A standard as capable of serving all of the low-voltage applications in a residence. These include: voice (telephone, computer modem and fax), video (baseband for surveillance and broadband for cable-TV or satellite), data (a LAN), alarm and security devices (dial-out for fire and burglar alarms) and home automation control of HVAC and lighting.

You can then connect EIA-600 compliant home-automation devices into the structured cabling system as needed. Finally, home theater/entertainment equipment can be interconnected using 1394-compliant patch cords with plug-and-play use.

Everyone recognizes the opportunity today for low-voltage installers in the residential wiring market. Contractors who already have been placing low-voltage systems in homes have a leg up on this business, as do installing electrical contractors. Many vendors, sometimes in collaboration with distributors, offer training in residential wiring systems.